Magneto circular dichroism

Transketolase from Baker s yeast, easily split into TPP and apoenzyme, consists of 2 identical subunits of 70000 daltons. 2 TPP molecules are bound per mole of enzyme in a reversible manner. All coenzyme analogs tested turned out to be inhibitory to the enzymatic activity. A very high affinity was found for oxi-TPP and tetrahydro-TPP. There is evidence for a charge transfer complex between a tryptophan residue of apo-transketolase and TPP from fluorescence quenching and circular dichroism measurements. The chemical modification of the tryptophan residue at the coenzyme binding site supports this concept. The decrease of the magneto circular dichroism band at 292 nm after the reaction of apo-TK with the dimethyl (-2-hydroxi-5-nitrobenzyl) sulfonium chloride is regarded as direct evidence for the modification of a tryptophan residue. 

Optical rotatory dispersion and circular dichroism (83, 84) can often be of great value, and the spectra are particularly sensitive to the conformation of the protein. Much work remains to be done in this field before the results can be definitely interpreted in terms of the electronic structure of the metal. Magneto-optical rotation and magnetic circular dichroism (MOR and MCD), which are beginning to be applied to porphyrins and haemoproteins, offer much greater promise (30, 85). 

In the next section we summarize the theoretical background for coupled cluster response theory and discuss certain issues related to their actual implementation. In Sections 3 and 4 we describe the application of quadratic and cubic response in calculations of first and second hyperpolarizabilities. The use of response theory to calculate magneto-optical properties as e.g. the Faraday effect, magnetic circular dichroism, Buckingham effect, Cotton-Mouton effect or Jones birefringence is discussed in Section 5. Finally we give some conclusions and an outlook in Section 6. 

The geometrical arrangement indicates the relationship to the magneto-optical Kerr effect (MOKE). MCDAD corresponds to the longitudinal, MLDAD to the transversal MOKE. Additionally, the Earaday effect can be included it is the analogue to the magnetic circular dichroism in absorption (XMCD). 

Suryanarayanan et al. (1972) have shown that the results obtained by magnetic circular dichroism are in good agreement with those of Holtzberg and Torrance (1971). The lattice parameter of the fee unit cells are 6.20 A for SmSe and 6.60 A for SmTe. Magneto-optical properties have been reported by Paparoditis and Suryanarayanan (1972). 

In another paper Paparoditis et Suryanarayanan (1972) have reported the magneto-optical properties of thin films codeposited on heated substrates (67(1-770 K). They have shown that the properties depend especially on the Se concentration. Suryanarayanan et al. (1974) have studied YbTe films in more detail by optical absorption and magnetic circular dichroism. They proposed an energy level diagram, and concluded that the f-levels of ytterbium are located between the valence and conduction bands. These optical properties can be linked to a S.C.-M.-type transition, like the one observed at high pressures (150-190 kbar). 

Magneto-optical rotation and magnetic circular dichroism 48... 

Besides absorption and emission measurements, other techniques (optical, magnetic or magneto-optical) can also be used for determination and assignment of crystal-field energy levels inside the 4f shell two-photon absorption (TPA), Zeeman effect spectroscopy, electron paramagnetic resonance (EPR) and magnetic circular dichroism (MCD). 

---